Properly steam flaking corn can improve its nutritive value from 3 to 10% depending on the percent damaged grain, moisture content, fines, flake density, etc. (Karr, 1984, Zinn, 1990ab). An average improvement of 6% from correctly steam flaking corn potentially realized an estimated $750 thousand (to as much as $1.5 million) annually on 30 thousand head of feedlot cattle (Karr, 1984). Karr (1984) also reported the cost of a feedlot producing flakes with a density of 22 lbs/bu would be approximately $6.67/ton compared with $3.33/ton for flakes weighing 29 lbs/bu. Smith and Richardson (1996) reported the electrical cost of flaking corn at steam times of 20, 30, and 40 min was $2.30, $1.40, and $2.30 per ton for flakes weighing 26.0, 26.1, and 27.0 lbs/bu, respectively. They reported that after 40 min of steaming, the time required to roll 50 lbs of corn increased because of increased doughing on the rolls possibly because of overcooking the starch. This may also partially explain the increase in the cost of flaking corn steamed for 40 minutes.
Zinn (1 990a) examined the influence of steaming time on the digestion of flaked corn in steers consuming 75% corn diets (intake was restricted indicating digestibility may be higher than that observed for cattle consuming free choice). He compared steaming times of 34, 47, and 67 minutes and flaked corn to a density of 25-26 lbs/bu. Moisture uptake was similar for corn steamed at 34 and 47 minutes, averaging 5%. Moisture uptake by corn steamed for 67 minutes was 8% (i.e. significantly higher). Zinn (1990a) indicated the initial 3 to 5 percentage unit increase in moisture occurs very quickly following application of steam and that moisture greater than 5 percentage units requires prolonged exposure to steam. Prolonged steaming and/or lack of penetration increases external moisture on the corn kernel which too contributes to doughing on the rolls (Karr, 1984). In general, steaming corn longer than 34 minutes did not increase the nutritive value of the corn and total G.I. tract digestibility of starch was essentially complete (99.5%) for steam flaked corn steamed for 34 minutes.
The main purpose for steam flaking is to increase the digestibility of the starch and to maximize net energy intake by the cattle. Feedlot growth trials have shown steam flaking will increase the energy value of corn over that of dry rolling from 13 to 16 % (Zinn, 1987). The degree improvement in starch but not performance has been linearly related to flake thickness and/or density (Osman et al., 1970, Zinn, 1990b). Zinn (1990b) compared the feeding value of corn steam flaked to densities of 28, 24, and 20 lbs/bu. He reported flake density was directly related to thickness and inversely related to in vitro enzymatic starch digestibility (IVSD) and suggested the relationship between IVSD and in vivo starch digestion may be casual rather than causal. Ruminal and total tract starch digestibility increased with decreasing flake density but was of a small magnitude (1.1%) for flakes weighing 28 compared with 20 lbs/bu. Therefore, differences in digestibility between flakes weighing 24 and 20 lbs/bu would likely be even less.
Feedlot performance did not differ for steers fed diets containing corn flaked to densities of 28, 24, and 20 lbs/bu (Zinn, 1990b). In fact, Zinn (1990b) reported a tendency for slower weight gain, and reduced feed efficiency by steers fed steam flaked corn of the lowest density (20 lbs/bu). Steers consuming the lighter flakes had significantly lower ruminal pH, suggesting digestive dysfunction and reduced performance of some individual animals in the study. Variation in weight gain for steers consuming the 20 lbs/bu flake was 366% greater than the average for both groups of steers consuming the 24 and 28 lbs/bu flakes which suggests the variability in weight gain was due to the variable effects of 20 bushel weight corn on gastrointestinal tract function and subsequent performance. In addition to digestive dysfunction, the tendency toward reduced performance by cattle consuming flakes of the lowest density was attributed to reduced intake and consequent reduced weight gain rather than lower feed conversion. This type of situation was addressed by Karr (1984) who suggested if grain utilization is improved 15% we would hope feed consumption would not decrease more than 8% so that a faster rate of gain could be attained through greater net energy intake.
Many factors influence starch availability (i.e. degree of processing) including corn quality, tempering conditions, cook time, cook temperature, roll condition, and flake density. Unfortunately, commercially available methods that are currently being used to measure processing degree of grain are unreliable and unscientific. Flaking corn is an expensive process; too little processing may produce flakes with only little improvement in starch availability, while over-processing may produce flakes with very high starch availability, thereby increasing production costs and the potential for digestive upset with little if any improvement in cattle performance.
The most common commercially available method for determining starch availability is to simply measure gas production by yeast fermentation. Many commercial laboratories provide this service; however, methods and results vary greatly between and within laboratories due in part to differences in methodology, enzyme activity, and lack of use of a meaningful standard and an accounting of initial corn quality. For example, laboratory results will vary because the total starch content of corn varies between areas and seasons, and because the activity of enzymes will vary between suppliers as well as pH. If an attempt to control these sources of variation is not made, then estimates of starch availability (or degree of processing, or percent gelatinization) are highly variable due to the corn itself and laboratory methodology rather than milling practices. Therefore, it is not surprising why results will vary widely between and within laboratories, which may serve only to confuse and frustrate the miller.